Manufacture of tanning substances



3. beech-wood sulphite waste lye of 33 Baum with 40 parts of solid caustic soda at 90 to 100 C., while stirring, for 6 to 8 hours.

The obtained tanning substance can be used by itself, without addition of other substances,

for tanning purposes and is practically com-- The process according to the invention has therefore the advantage of a practically complete utilization of the sulphite cellulose waste lye, since the following substances are obtained:

(a) A practically completely soluble tanning substance representing 60 to 70 per cent. of the pletely soluble in warm water with a yellow-" I brown color. The solution has a-pI-I-value of 3 to 4 and may be used according to the usual tanning prescriptions. The tanning substance is absorbed almost completely by the normally treated hides. The leather obtained is light-brown, has a slightly aromatic smell, good strength, and soft quality.

A further advantage of our process consists in that owing to the careful low temperature treatment with alkali, not only the tanning substances of advantageous properties, but other valuable products can be obtained in the courseof this process. These products are destroyed -cOmpleteIy-orfor the greatest part, if tanning substances are obtained-from sulphite waste lye by a more intensive action of alkali. Such byiprod'ucts are, first of all, hydroxyand alkoxyaldehydes, especially vanillin, as well as sugar '..:acting' as a reducing agent, and organic acids. s-Hydroxyand alkoxy-aldehydes are obtained l.-.fr.om the mother liquor remaining after the separation of the tanning substance, according to methods knownper se, e. g. by extraction with organic solvents. or by steam distillation, a remaining solution rich in reducing, sugar-like :substances and organic acids being obtained.

.- '..In order to avoid losses of hydroxyand alk- ..oxy+aldehydes when separating tanning substances from the mixture obtained by an alkali =.,treatment of the sulphite waste lye or the like at relatively low'temperatures, acid, preferably hydrochloric acid, is added in such an amount that only bisulphite and a small quantity of free sulphur dioxide are formed in the acidified mixture, whereas the presence of free mineral .acid is avoided, since such acid would decompose. the .bisulphite compounds of the hydroxyaand alkoxy-aldehydes split off from the lignin in.'the secondary reaction, and would result in -.a'iseparation of the aldehydes together with the ..tanning substance in insoluble form. The acidigfication of .the mixture for separating the tan- :ning substance is' therefore only carried to a pH-value of 5. Only after the separation of 5-; thetanning substance has occurred, the solution r...should be further acidified. If, for instance, an extraction process is used to obtain the aldehydes, the mother liquor deprived from the tan- ...ning substance, is adjusted to a pH-value lower than 5, preferably to a pH-value between, 2 and 3. Before, or after, the aldehydes are obtained,

. the solution may be evaporated and the mineral salts, normally sodium chloride, may be obtained by crystallizing and centrifuging or the like.

-The separated salts. may be used as tanning salts.

The residue which may be concentrated by evaporation at a suitable pI-I-value such as a pH- 1 value of 5, represents a rather'thick liquid of amounts of highly reducing,

greyish-brown color, which still contains large sugar-like substances, as well as various organic acids and may be employed as a reducing agent for technical purposes, for instance to reduce metallic salts in galvanic processes, manufacture of dyes, vatdyeing and soon, and can substitute the substances, suchwas glucose, hyposulphite and the like-used heretofore inthese domains.

organic dry substance of the sulphite cellulose waste lye or its residue, which substance may, under normal tanning conditions, be employed as the only tanning means in the process.

(1)) A large part of the sulphur contained in the initial material, particularly of the organ- Examples (1) 125 parts by weight Or thickened sulphite spirit residuec'ontaining 32.4 per. cent. or-

. ganic' dry substance, are treated at normal temperature in a kneader with 40 parts of solid caustic soda which are gradually added. By proper. control of the alkali addition, a temperature of 90 to 100 C. is reached which .is

maintained throughout the following 6 to '8 hours. .During that period, the mixture is being stirred and becomes thicker and darker. It

isthen diluted with water inthe amount of one third of the volume, whereafter a pI-I-value of 5 is adjusted with hydrochloric acid, the disengaged tanning substances are filtered off and washed in the cold with 0.5 per cent.. bydrochloric. acid and thereafter with water. 28 parts by weight of a dry tanning substance are 5 obtained. The mother liquor remaining from the filtration is mixed with the washing liquid and heated, while the escaping sulphur dioxide is collected. From'the remaining acid solution,

- in which the pH-value'is adjusted to 2-3, the

hydroxy-. and alkoxy-aldehydes liberated from their bisulphite compoundsfare obtained asyellow oils by known extraction methods with organic solvents (chloroform, ether, methylene chloride'and so on). The yield amounts to 3 parts by weight. The aqueous solution is then neutralized with alkali and concentrated by evaporationto. such'an extent that the dissolved sodium chloride is precipitated; There remain 18 parts by weight of a liquid which may be used as a reducing agent. r

(2) 130 parts by weight of athickened spruce,- wood sulphite waste lye containing 34.7 per cent. organic dry substance are stirred at the conditions of the Example 1 with 67 parts by weight of per cent. strong lye at to C. for 6 to 8 hours, and the resultingmixture is worked up acording to Example 1. The yields amount to 30 parts by weight of tanning substance, 5 parts by weight of a mixture of aldehydes, 20 parts by weightofa reducing agent.

(3) 128 parts of a thickened beech-wood sulphitewastelye containin 38 per cent. of organicdry substance arestirred. at the conditions of Example 1 with 40 parts ofsolidcaustic soda at 90 to 100 C; for 6 to 8.hours. By further working: up. the. resulting mixture according to Example l, 31 parts by weight of. a tanning substance; .8 parts by. weight ofa .mixture .of. alde-.

agent, are obtained.

hydes, and lfi -partsiby zweighigg of a reducing In 'order' to separate -the tanning, substances from the solution diluted with water; relatively large amounts'ofimineral. acids. are. consumed in, thisprocess, irrespective.,ot -.,-the particular.,con-

, -,ditions.maintained inthe, alkali treatment, since the entire amount of alkali .subjected'to'the reglaction must be combined withethe aci ,the tannin substance isliberated from its}.alkali m given 'in' the: gexamplesygper, ;1 parts zof;--,sul-

compounds. However, it. is possible to s,eparate the tanning substances from.,the solution-under conditions that will enableusto save, aponsid- .erable. amount of mineral acidgwith concurrent,

lrrinihezh e -imina r sepa atiomm ;sbemsedeas harmea se r,.asza cadd tio lWa hin lmeansaduerto ts c nte t. of rbona s, bicar- --cbona s.za drsanoni e like su s nc .ln; t e claims; sle res on' iconcent ated ncaustic. alkah. when ,noteoth w e. specified: i intended to define concentrations n ;the,;.;order .nofnabout .parts .brwe ht f;.=.caust c alka i (correspondin s sabo t parts vmmmen phite cellulose waste lye of,- about 30?,1,B..

Theexpre n:;su phi eece l ewwas esir ei th 1ai sis' n end dtold fl e aiconcen rated lawastezl sof .ahe tfi tjtBaum i lu ngswa t partial recovery of' the excessive alkali in fornr qgg lye residues whichmemainaitenthe extractiomof of valuable compounds.

For this purpose the diluted solution resulting from the treatment of the sulphite waste lye or its residue with alkali is subjected to a saturation with carbon dioxide or gases containing carbon dioxide, before the taming substances are liberated by the acid treatment. The process is preferably carried out so that the saturation with carbon dioxide is effected in two stages by introducing first carbon dioxide, until a pH- value of 9 is attained; in this stage substantially sodium sulphite and sodium sulphate are precipitated together with slight amounts of soda. After separating the mixture of salts (fraction I) the saturation with carbon dioxide is continued in a second stage, until a pH-value of about 7.5 is reached. A mixture of bicarbonates with some soda precipitate is thus obtained, which includes at the same time a considerable amount of saponine substances of high lathering power, (fraction II) By the described saturation with carbon dioxide and the preliminary separation of the precipitated salts, about two thirds of the alkali present are removed from the solution so that 40 the amount of mineral acid necessary for complete combination with the remainin alkali will be only one third of the amount required otherwise. After elimination of the salts formed in the reaction, the solution still contains the alkali compounds of the tanning substances, and, especially when working up beech-wood, considerable amounts of sodium acetate. For liberating the tanning. substances, the solution is now acidified, preferably up to a pH-value of 3.5 in a manner known per se. The acidification may be efiected by mineral acids, such as hydrochloric, sulphuric or phosphoric acid. The use of sulphuric or phosphoric acid to liberate the tanning substances from their alkali compounds is particularly advantageous, since in such a case the liquid which is obtained, after the precipitated substances are filtered or centrifuged off, may be subjected to a distillation, if desired after being strongly acidified once more, in order to obtain acetic acid in the distillate.

The carbon dioxide required in the course of the process for saturation and preliminary separation, is available in large quantities in paper mills and cellulose factories. There, the sulphite waste lye to be worked up accumulates, since in the manufacture of the waste lye of calcium bisulphite from lime stone and sulphurous acid, this lye bein used for disintegrating purposes, carbon dioxide escapes from the lye-towers as a waste gas. The mixture of sodium sulphite and sodium sulphate, accumulating as fraction I can be returned into the process by admixing this mixture of salts to the water in the lyetowers.

The mixture accumulating as fraction spirit or the like.

What- .we. cla rm-i 1. A procession pmducing tanning substances iromiesulphite cellulose. waste; lyemwhich-wcomprises treatin said waste lye in fOIIHsOi: arconcentrated liquor of about 30 B. with concentrated caustic alkali solution containing at least 60 per cent of alkali hydroxide, maintaining the alkaline solution under atmospheric pressure at 25 a temperature ranging from 60 to C. for

several hours, precipitating from the alkaline solution the tanning substances which formed during said treatment by addition of hydrochloric acid in an amount imparting a pH-value of about 5 to the resulting liquid, and removing the tanning substances from said liquid.

2. A process for producing tannin substances from sulphite cellulose waste lye, which comprises treating said waste lye in form of a concentrated liquor of about 30 B. with caustic alkali in a ratio of about 30-32 parts of caustic alkali, calculated a solid alkali hydroxide, per 100 parts of said concentrated liquor, said liquor containing from about 30-38 per cent of dry organic substances, maintaining the alkaline solution thus formed under atmospheric pressure at a temperature ranging from 60 to 100 C. for several hours, precipitating from the alkaline solution the tanning substances formed during the treatment by addition of hydrochloric acid in an amount imparting a pH-value of about 5 to the resulting liquid, and removing the tanning substances from said liquid.

3. A process for producing tanning substances from sulphite cellulose waste lye, which comprises treating said waste lye in form of a concentrated liquor of about 30 B. with concentrated caustic alkali at a temperature ranging from 60 to 100 C. for several hours under allmospheric pressure, precipitating from the alkaline solution the tanning substances formed during the treatment by addition of hydrochloric acid in an amount imparting to the resulting liquid a pH-value of about 5, removin the tanning substances from said liquid, adding more acid to bring the pH-value of the liquid to 2-3, and extracting therefrom the hydroxyand alkoxy-aldehydes present therein.

4. A process for producing tanning substances 0 saturating the alkaline solution with carbon dioxide in two stages, introducing the carbon dioxide in a first stage until a pH-value of about 9 is reached in the solution, separatin from the liquid the formed mixture of sodium sulphite, sodium sulphate, and sodium carbonate, then from sulphite cellulose waste lye, which comintroducing carbon-dioxide in said second stage until-the pH-value reaches about 7.5, separating from the liquid the formed carbonates, bicarbonates, and saponine-like substances, there-- 4 after acidifying the liquid for precipitation of. the tanning substances and separating the same from the liquid.

5. A process accordingto claim 4, wherein the caustic soda is added in form of solid NaOH in a ratio of about 30-32 parts to 100 parts of the concentrated liquor.

6.- A process according to claim 4, wherein the caustic soda is added in form of a concentrated solution of at least 60 per cent NaOI-I, in an amount of about 30-32 parts of NaOI-I for 100 parts of concentrated liquor.

MICHAEL MANGO-Ll).

, HILDA Administratrizc of the Estate of Fritz Neubyer,

Deceased.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Honig May 6, 1941 

1. A PROCESS FOR PRODUCING TANNING SUBTANCES FROM SULPHITE CELLULOSE WASTE LYE, WHICH COMPRISES TREATING SAID WASTE LYE IN FORM OF A CONCENTRATED LIQUOR OF ABOUT 30* BE. WITH CONCENTRATED CAUSTIC ALKALI SOLUTION CONTAINING AT LEAST 60 PER CENT OF ALKALI HYDROXIDE, MAINTAINING THE ALKALINE SOLUTION UNDER ATMOSPHERIC PRESSURE AT A TEMPERATURE RANGING FROM 60 TO 100* C. FOR SEVERAL HOURS, PRECIPITATING FROM THE ALKALINE SOLUTION THE TANNING SUBSTANCES WHICH FORMED DURING SAID TREATMENT BY ADDITION OF HYDROCHLORIC ACID IN AN AMOUNT IMPARTING A PH-VALUE OF ABOUT 5 TO THE RESULTING LIQUID, AND REMOVINGG THE TANNING SUBSTANCES FROM SAID LIQUID. 